1. Field of the Invention
The present invention relates to carbon nanomaterials and their therapeutic and cytotoxic uses thereof. More specifically, the present invention relates to using multiwall carbon nanomaterials for the treatment of cancer and other diseases. The present invention also relates to carbon nanomaterials and methods for measuring their toxicity thereof.
2. Related Art
The emerging field of nanotechnology is part of a new industrial revolution being applied to a diverse array of consumer products and medical applications, ranging from cosmetics to electronics and to drug delivery vehicles. With this revolution, methods to reduce the potential toxic effects of nanoparticles in both the environment and for medical applications should be addressed. Defining any potential toxicity will aid the nanotechnology industry to minimize the environmental impact of nanomaterials, leading to reduced concern from the public and policymakers, and a more successful industry.
The increasing use of nanotechnology in consumer products and medical applications underlies the importance of understanding its potential toxic effects to people and the environment. Although both fullerene and carbon nanotubes have been demonstrated to accumulate to cytotoxic levels within organs of various animal models and cell types, and carbon nanomaterials have been exploited for cancer therapies, the molecular and cellular mechanisms for cytotoxicity of this class of nanomaterial are not yet fully apparent.
Material that does not manifest toxic or carcinogenic characteristics in regular forms may have altered physical/chemical properties due to the quantum effect when their feature sizes fall in the 1-100 nm range that define them as nanomaterials. The transport and persistence of nanomaterials in the environment might be drastically different from the bulk material that we are familiar with, and new biological mechanisms for interaction, uptake and metabolism of nanomaterials have begun to emerge in the last few years. The unique properties of the nanomaterials include the increased surface/mass ratio, different shapes with size scale at the same range as biomolecules, altered mechanical and electromagnetic properties. It is critical to identify potential toxic/carcinogenic features of manufactured nanomaterial early in the process so that proper precautions can be taken before long term damages are done.
Carbon nano-materials, including carbon nanoparticles and nanotubes, have been one of the most extensively used nanoparticles, because of their unique and superior properties, including large surface areas, high electrical conductivity, and excellent strength. Multiwall carbon nanotubes (MWCNTs) and multiwall carbon nano-onions (MWCNOs), which will be the focus of this study, represent a relatively recently discovered allotrope of carbon derived from the more intensively studied fullerene (C60). Single-walled, double-walled and multi-walled MWCNTs, with their diverse chemical and physical properties, have led them to be used in applications ranging from nanowires, electronic components, catalyst supports, electronic displays to drug delivery, and may even be used for hydrogen storage. Giant, nested fullerenes, generally called nano-onions (MWCNOs), comprise the least studied class of carbon nanoparticles. MWCNOs are usually produced by an underwater carbon-arc discharge. Although the applications of MWCNOs have lagged behind those of MWCNTs, they have been used as components of nanocomposites for applications including solar cells, light-emitting devices, and in fuel-cell electrodes.
The increase in commercial interest of nanomaterials and their subsequent production en masse, will lead to greater potential for exposure, to individuals. Fortunately, aerosol release of the MWCNOs and MWCNTs during manufacturing is limited. However, because of the increase in use, the risk associated with exposure and the molecular mechanisms of any cytotoxicity need to be well understood. Some of the primary questions that should be addressed include: i) likely routes and location of exposure, ii) molecular mechanisms of toxicity induced by exposure, iii) does observed toxicity correlate most to size, shape, or composition, iv) is there any concentration-dependent toxicity and v) are byproducts of production or decomposition toxic. The scientific community is beginning to address these concerns, but information is scant. To date, most toxicity studies have been performed, on ultrafine particles, which, interestingly, are more toxic than equivalent micron-sized material. See Silva, V. M., Corson, N., Elder, A. & Oberdorster, G. The Rat Ear Vein Model For Investigating In Vivo Thrombogenicity Of Ultrafine Particles (Ufp). Toxicol Sci (2005). Other studies, however, have demonstrated that toxicity is more highly correlated with particle composition and surface chemistry rather than size. See Sayes, C. M. et al. The differential cytotoxicity of water-soluble fullerenes. Nano Letters 4, 1881-1887 (2004).
Recently, single-walled carbon nanotubes (SWCNT) have been demonstrated to be an effective infrared photosensitizer for cancer cells (Shi Kam, N. W., O'Connell, M., Wisdom, J. A. & Dai, H. Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction. Proc Natl Acad Sci USA 102, 11600-11605 (2005)), and C2B10 carborane cage-coated SWCNT has been constructed as the delivery vehicle for boron neutron capture therapy for cancer (Yinghuai, Z. et al. Substituted carborane-appended water-soluble single-wall carbon nanotubes: new approach to boron neutron capture therapy drug delivery. J Am Chem Soc 127, 9875-9880 (2005)). Fullerene has been suggested to be a promising carcinotoxic chemical (Sayes et al., Nano Letters 4, 1881-1887 (2004); and Burlaka, A. P. et al. Catalytic system of the reactive oxygen species on the C60 fullerene basis. Exp Oncol 26, 326-327 (2004)). Therefore, we speculated that multi-walled carbon nanomaterial such as MWCNO and MWCNT will be more effective cancer killing agent than the SWCNT and single-walled fullerene. It is even more important to decipher the cytotoxicity and molecular mechanism of the multi-walled carbon nanomaterials.
Early studies have indicated that a repeated subchronic topical dose of fullerenes on mouse skin for up to 24 weeks, after initiation with a polycyclic aromatic hydrocarbon, does not result in either benign or malignant skin tumors, in contrast to development of benign skin tumors when a phorbol ester control is used for promotion (Nelson, M. A. et al. Effects of acute and subchronic exposure of topically applied fullerene extracts on the mouse skin. Toxicol Ind Health 9, 623-630 (1993)). More recent studies have begun to indicate possible adverse effects from carbon nanomaterial exposure, including oxidative stress, accumulation in nasal cavities, lungs, and brains after inhalation, inflammation, and tissue damage and central nervous disorders.
Evidence thus far suggests that the key factors contributing to nanomaterial-related cytotoxicity are size/mass, shape, surface charge, and surface functionalization. The cytotoxicity with equal mass basis shows an order of: SWNTs>MWNT10>C60 (Jia, G. et al. Cytotoxicity of Carbon Nanomaterials Single-Wall Nanotube, Multi-Wall Nanotube, and Fullerene. 39, 1378-1383 (2005)). Investigations with 2 nm gold nanoparticles in different cell types, tested by MTT, hemolysis, and bacterial viability assays, showed that surface charge was a key factor in inducing toxicity. This indicates that cationic nanoparticles are moderately toxic, and have an immediate toxic effect at the Blood Brain Barrier, whereas anionic particles are relatively nontoxic (Goodman, C. M., McCusker, C. D., Yilmaz, T. & Rotello, V. M. Toxicity of gold nanoparticles functionalized with cationic and anionic side chains. Bioconjug Chem 15, 897-900 (2004); and Lockman, P. R., Koziara, J. M., Mumper, R. J. & Allen, D. D. Nanoparticle surface charges alter blood-brain barrier integrity and permeability. J Drug Target 12, 635-641 (2004)). Different surface coating also has been shown to change the cytotoxicity profiles of quantum dots (CdSe nanocrystals) dramatically, and modifications may attenuate the toxicity (Kirchner, C. et al. Cytotoxicity of colloidal CdSe and CdSe/ZnS nanoparticles. Nano Letters 5, 331-338 (2005)).
As the exact molecular mechanisms for the damages inflicted are still not fully understood, the urgency of a more thorough molecular characterization of nanomaterial toxicity is evident. Expression array analysis and phenotypic measurements of exposed cell populations may provide insight into the mechanisms responsible for adverse events observed in these models. For example, a recent preliminary unpublished investigation demonstrated gene expression changes associated with the toxicity of nanoscale materials (Cunningham, M. J., Magnuson, S. R., Falduto, M. T., Balzano, L. & Resasco, D. E. Investigating the toxicity of nanoscale materials by gene expression profiling: A systems biology approach. American Chemical Society Annual Meeting Presentation (2005), and thus the potential benefit for using microarray technology to perform high throughput characterization of nanomaterial toxigenomics.